1. Field of the Invention
The present invention relates to a particulate phyllosilicate mixture and use thereof. The particles of phyllosilicate mixture of the present invention possess excellent mechanical strength and abrasion resistance, permit creation of unfavorable phenomena impedimental to reactions and stable operations, such avoiding crumbling or powdering of particles, and in addition have excellent fluidity. Therefore, the particulate phyllosilicate mixture of the present invention is suitable as a catalytic component or as a catalyst.
Phyllosilicates have been extensively used as components for various catalysts or as catalysts per se, as additives for plastics, paints and the like, and, by virtue of excellent feel in use and feel to the hand, as additives for cosmetics and pharmaceuticals. In particular, in many cases, they have been used as a catalytic component or a catalyst for petroleum refining, various chemical reactions, including oxidation/reduction, hydrogenation, dehydrogenation, and alkylation, and polymerization of olefins on a commercial scale.
In general, in a reaction system utilizing a catalyst, for any of a gaseous phase and a liquid phase, the so-called "heterogeneous catalytic reaction" mainly takes place, and it is common practice to carry out the reaction in a fixed bed, a moving bed, a spouted bed, a suspended bed or the like. For this reason, for most of the catalysts used, shaping into particles is carried out from the viewpoint of improving the flow of the sting materials and/or the reaction products and the transfer of materials and heat, or alternatively a particulate carrier is prepared followed by supporting of a material, which is to serve as a catalyst, a co-catalyst or the like on the carrier. The particulate phyllosilicate mixture according to the present invention is particularly preferred as the above catalytic component or catalyst.
2. Background Art
In general, phyllosilicates, for both natural and synthetic products, when used in a powder form, are mechanically ground to a powder. Most of them have an irregular particle shape and a small bulk density, contain a large amount of fine powder, and have a wide particle size distribution. Phyllosilicates having such shape and powder properties, when used as a catalytic component or a catalyst, are likely to have poor fluidity, poor productivity, and render stable operation difficult due to the presence of the fine powder or the like, so far as the present inventors know.
Conventional methods for improving the shape of the above phyllosilicate include, for example, one which comprises dispersing a water-swellable clay mineral in water and spray-drying the dispersion to prepare granules (Japanese Patent Laid-Open No. 50311/1988), one wherein finely divided mica is heated at the melting temperature and then recrystallized (Japanese Patent Laid-Open No. 263431/1994), and one wherein acid-treated smectite clay is mixed and aggregated to prepare granules (Japanese Patent Laid-Open No. 263421/1994).
Among the above methods, the method using spray drying can simply provide a spherical powder having even particle diameters. This method, however, suffers from the following problems. Specifically, when the concentration of the aqueous dispersion of the water-swellable clay mineral is increased in order to improve the profitability, the viscosity of the slurry is increased to create clogging of nozzles or poor shape. On the other hand, when the concentration of the aqueous dispersion of the water-swellable clay mineral is decreased in order to maintain good viscosity of the slurry, only particles having a small diameter can be prepared, resulting in unsatisfactory productivity.
On the other hand, it has been known that olefins are polymerized with catalysts based on (1) a metallocene compound combined with (2) an aluminoxane as disclosed in Japanese Patent Publication (which will be referred to herein as "Japanese Kokoku") No. 12283/1992, Japanese Patent Laid-Open Publication (which will be referred to herein as "Japanese Kokai") Nos. 19309/1988, 35007/1985 and 167307/1990. The polymerizations with these catalysts have advantages over those obtainable when conventional Ziegler-Natta catalysts are used in that a very high catalyst activity per the transition metal used and polymers having sharp molecular weight distribution and compositional distribution are obtainable.
However, these catalysts are often soluble in the polymerization system, and this feature may sometimes result in process problems such that the olefin polymers obtained by slurry polymerization or vapor/gas phase polymerization in a particulate form may sometimes have poor granulometric characteristics such as an irregular form of granules, lower bulk densities and higher contents of fines. Furthermore, since these catalysts require higher amount of aluminoxanes when commercially acceptable catalyst activities are required, whereby the activities per the aluminum used are low thus entailing economical problems and necessity of removal of the catalyst residues from the polymers produced.
Some improvements have been proposed to solve these problems. For instance, it is proposed to support one or both of the transition metal compound and the organoaluminum compound on an inorganic oxide such as silica or alumina or on an organic material thereby conduct polymerization of olefins thereover. See Japanese Kokai No. 35007/1985, No. 135408/1985, No. 31404/1986, No. 108610/1986, No. 276805/1986, No. 296008/1986, No. 101303/1989, No. 207303/1989, No. 74412/1991, No. 74415/1991, No. 234709/1991 and No. 501869/1981 (PCT). It is also proposed to subject the supported catalysts to preliminary polymerization. See Japanese Kokai No 234710/1991.
These prior proposals would still entail some problems such that the polymers so produced contain fines or granules of a larger size and have low bulk densities and that the polymerization activities per the solid component of the catalysts are low. Other improvements have also been proposed such that use as catalysts is made of metallocene compounds and aluminoxanes supported on the smectite (Japanese Kokai No. 25214/1993) and use as polymerization catalysts of metallocene compounds, phylloclay minerals which have undergone treatment with metal oxides or precursors to metal oxides followed by calcination and organic aluminoxanes (Japanese Kokai No. 33814/1995).
These improvements proposed may produce satisfactory catalyst activities per the aluminum used, but some problems may still remain unsolved in commercial operation such as crushing of particles or formation of fines depending on the polymerization conditions employed resulting in the lowering in the bulk density of the polymer powder or in the lowering in the fluidity in the vapor phase polymerization. The formation of fines may sometimes cause adhesion of the polymers to or sheeting on the polymerization vessel walls, or cause the clogging within pipings or heat-exchangers used whereby stable operation may sometimes be hindered.
The improvements proposed by the present inventors referred to hereinabove to the granulation of phyllosilicates as disclosed in Japanese Kokai Nos. 301917/1993 and 228621/1995 would not always be fully satisfactory when the phyllosilicates so granulated are used as catalyst supports as referred to hereinabove.
In order to solve the above problems, the present inventors ever granulated the phyllosilicate which had been treated under the specific requirements. As a result, the resultant particles had good powder properties, that is, contained no significant amount of fine powder and coarse particles and had high bulk density (Japanese Patent Laid-Open Nos. 301917/1993 and 228621/1995). However, when a phyllosilicate, which is flaky and has a relatively large particle diameter, such as a phyllosilicate belonging to the mica group is used, even though it could be successfully granulated, the resultant particles often have small bulk density and unsatisfactory strength. Therefore, the particles prepared by the above modified method, when used as a catalyst carrier, is not always satisfactory in the productivity of a contemplated polymer, creation of a fine powder and the like.